Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface, showing the new design.

The outer broken line rectangle shows the display screen portion, depicts the bounds of the claimed design, and forms no part thereof. All other broken lines show portions of the article and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 